The current technique for determining dynamic pressure in blast waves is subject to large errors below incident shock over pressures of 69 kPa (10 psi). It is shown that if a single pressure-sensing element can be used to measure the differential pressure between stagnation and side-on overpressures, then dynamic pressure can be determined with much less error. A design for a differential pressure gage is presented. A particular diaphram size and material are proposed, and several diaphram deflection-sensing techniques are indicated. The frequency response of the gage seems adequate for measurements of blast waves from large HE charges.